title: Criterion validity and accuracy of global positioning satellite and data logging devices for wheelchair tennis court movement.
abstract: OBJECTIVE
  To compare the criterion validity and accuracy of a 1 Hz non-differential global positioning system (GPS) and data logger device (DL) for the measurement of wheelchair tennis court movement variables.
  
  
  METHODS
  Initial validation of the DL device was performed. GPS and DL were fitted to the wheelchair and used to record distance (m) and speed (m/second) during (a) tennis field (b) linear track, and (c) match-play test scenarios. Fifteen participants were monitored at the Wheelchair British Tennis Open.
  
  
  RESULTS
  Data logging validation showed underestimations for distance in right (DLR) and left (DLL) logging devices at speeds >2.5 m/second. In tennis-field tests, GPS underestimated distance in five drills. DLL was lower than both (a) criterion and (b) DLR in drills moving forward. Reversing drill direction showed that DLR was lower than (a) criterion and (b) DLL. GPS values for distance and average speed for match play were significantly lower than equivalent values obtained by DL (distance: 2816 (844) vs. 3952 (1109) m, P = 0.0001; average speed: 0.7 (0.2) vs. 1.0 (0.2) m/second, P = 0.0001). Higher peak speeds were observed in DL (3.4 (0.4) vs. 3.1 (0.5) m/second, P = 0.004) during tennis match play.
  
  
  CONCLUSIONS
  Sampling frequencies of 1 Hz are too low to accurately measure distance and speed during wheelchair tennis. GPS units with a higher sampling rate should be advocated in further studies. Modifications to existing DL devices may be required to increase measurement precision. Further research into the validity of movement devices during match play will further inform the demands and movement patterns associated with wheelchair tennis.
authors.affiliation: The University of Salford, Salford, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Sindall
authors.forename: John P
authors.initials: JP
authors.lastname: Lenton
authors.forename: Katie
authors.initials: K
authors.lastname: Whytock
authors.forename: Keith
authors.initials: K
authors.lastname: Tolfrey
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Oyster
authors.forename: Rory A
authors.initials: RA
authors.lastname: Cooper
authors.forename: Victoria L
authors.initials: VL
authors.lastname: Goosey-Tolfrey
mesh_terms: D054874:Athletic Performance / Q000502:physiology; D001330:Electronic Data Processing; D005260:Female; D040362:Geographic Information Systems; D006801:Humans; D008297:Male; D009068:Movement; D056888:Patient Positioning; D015203:Reproducibility of Results; D013715:Tennis; D014910:Wheelchairs